In-situ gasification of soot contained in exothermically generated syngas stream

ABSTRACT

A system is set forth for the exothermic generation of soot depleted syngas comprising (i) reacting a hydrocarbon-containing fuel with an oxygen containing gas in a first reactor to produce the syngas and byproducts comprising CO 2 , H 2 O and soot; and (ii) introducing the syngas and byproducts into a second reactor containing a non-carbonaceous material that traps the soot for a sufficient time such that the majority of the byproduct soot is gasified via reaction with the byproduct CO 2  and/or H 2 O to produce a syngas stream that is depleted in the soot. The system is particularly suitable for the practice of heat exchange reforming wherein a portion of the heat is recovered from the soot depleted syngas stream and used as at least a portion of the heat to facilitate the additional production of syngas via the (endothermic) catalytic reforming of natural gas and steam.

BACKGROUND OF THE INVENTION

Synthesis gas comprising carbon monoxide and hydrogen (hereafter syngas)is commonly produced by the partial oxidation (POX) of ahydrocarbon-containing fuel (hereafter, the POX process). The POXprocess is a highly exothermic process and produces a syngas stream attemperatures typically in range of 2100 to 2800° F.

A key challenge in the POX process, especially for carbon heavy fuels,is the removal of the entrained solid carbon (hereafter soot) producedas an undesirable byproduct. In particular, the soot that is generatedin the POX reactor will tend to foul conventionally designed heatexchangers that are used to recover a portion of the heat from theexothermically generated syngas stream. Although special boilers havebeen developed to process soot-containing syngas, these designs cannotbe readily transferred to heat exchange reforming wherein a portion ofthe heat is recovered from the POX generated syngas stream and used asat least a portion of the heat to facilitate the additional productionof syngas via the (endothermic) catalytic reforming of natural gas andsteam. Thus a system which can remove soot from syngas at hightemperature offers a key advantage to the practice of heat exchangereforming.

Typically, the soot is removed by quenching and scrubbing the syngaswith water. See for example EPO 648 828 B1 and WO 00/29323, bothassigned to Texaco Development Corporation.

Alternatively, JP 50040117 teaches directly filtering the syngas througha carbonaceous material that traps the soot for a sufficient time periodsuch that the oxygen containing molecules that are also produced asbyproduct in the POX process [i.e. CO₂ and H₂O] are given an opportunityto react with, and gasify, the soot. After such in-situ gasification ofthe soot, JP '117 introduces the syngas (or “reducing gas” as referredto therein) into a blast furnace.

A concern with the in-situ gasification scheme as taught in JP '117 isthe use of a carbonaceous material as the material for trapping the sootand subsequently allowing it to be gasified by reaction with thebyproduct CO₂ and/or H₂O. In particular, the carbonaceous material willbe susceptible to the very same gasification reactions that thecarbonaceous soot is intended to undergo (i.e. via reaction against thebyproduct CO₂ and/or H₂O). Consequently, a carbonaceous material willrequire more frequent replacing than a non-carbonaceous material.

The present invention addresses this concern by using a non-carbonaceousmaterial to trap the soot.

BRIEF SUMMARY OF THE INVENTION

The present invention is a system for the exothermic generation ofsyngas by the partial oxidation of a hydrocarbon-containing fuelcomprising:

-   -   (i) reacting the hydrocarbon-containing fuel with an oxygen        containing gas in a first reactor to produce the syngas and        byproducts comprising CO₂, H₂O and soot; and    -   (ii) introducing the syngas and byproducts into a second reactor        containing a non-carbonaceous material that traps the soot for a        sufficient time such that the majority of the byproduct soot is        gasified via reaction with the byproduct CO₂ and/or H₂O to        produce a syngas stream that is depleted in the soot.

DETAILED DESCRIPTION OF THE INVENTION

A key to the present invention is that the material used to trap thesoot in the second reactor is a non-carbonaceous material. This is keybecause if a carbonaceous material were used (i.e. such as in JP50040117), the material would be susceptible to the very samegasification reactions that the carbonaceous soot is intended to undergo(i.e. via reaction against the byproduct CO₂ and/or H₂O). Consequently,a carbonaceous material will require more frequent replacing than anon-carbonaceous material.

In a key embodiment of the present invention, the system furthercomprises a heat exchange reformer for recovering a portion of the heatfrom the soot depleted syngas stream and using at least a portion of therecovered heat to facilitate the additional production of syngas via the(endothermic) catalytic reforming of natural gas and steam.

Alumina is one example of the material that can be used as thenon-carbonaceous material in the present invention. Various otherrefractory materials such as zirconia or lanthana could also be used,optionally in combination with alumina. In one embodiment of the presentinvention, the material is packed in the second reactor in the form ofspherical particles to efficiently trap the soot without creatingexcessive pressure drop. The pressure drop and removal efficiency for anexample reactor consisting of 2 feet of 3 inch diameter spheres and 1foot each of 2 inch, 1 inch, and 0.5 inch diameter spheres has beencalculated. With a superficial gas velocity of 7 ft/s, the pressure dropis 16 psi while the removal efficiency is such that 85% of the sootparticles 21 microns in diameter are removed (larger soot particles areremoved almost completely and smaller particle are passed through thebed almost completely). By arranging the spherical particles in thismanner, soot particles of different sizes are trapped within each zone.This distributes the soot along the direction of flow and increases thecapacity of the bed to hold soot without plugging.

Alternate packing shapes such as rings could also be used to allow morecomplete removal of a wider range of soot sizes while minimizingpressure drop. In addition, the non-carbonaceous material could alsohave a catalytic functionality to facilitate the gasification of thesoot.

POX reactors can operate over a temperature range from about 1700 F to3500 F; however, the most common operating range is from about 2100 to2800 F. The system described here is preferentially operated in atemperature range from 2100 F to 2800 F. At higher temperatures, thehydrocarbon feed to the partial oxidation step is overly oxidized,resulting in less syngas and more byproduct CO₂ and H₂O. At lowertemperatures, there is a substantial amount of unconverted hydrocarbonfeed. Additionally at lower temperature, the quantity of soot held inthe packing becomes too great and the packing plugs. The systemdescribed here is designed to operate at a steady state in which thegasification rate is equal to the rate at which the soot is trapped. Forevery 100 F drop in temperature between 2500 F and 2100 F the quantityof soot which must be held on the bed for the gasification rate to equalthe amount of soot generated in the POX unit increases by approximatelyan order-of-magnitude.

It is within the scope of the present invention to include a fluidaddition step between the first and second reactors. Potential benefitsinclude managing the high temperatures and increasing the driving forcefor soot gasification. For example, steam could be added to the syngasand byproducts produced by the first reactor prior to introducing thesyngas and byproducts into the second reactor.

The skilled practitioner will appreciate that there are many otherembodiments of the present invention which are within the scope of thefollowing claims.

1. A process for the exothermic generation of syngas by the partialoxidation of a hydrocarbon-containing fuel comprising: (i) reacting thehydrocarbon-containing fuel with an oxygen containing gas in a firstreactor to produce the syngas and byproducts comprising CO₂, H₂O andsoot; and (ii) introducing the syngas and byproducts into a secondreactor containing a non-carbonaceous material that traps the soot for asufficient time such that the majority of the byproduct soot is gasifiedvia reaction with the byproduct CO₂ and/or H₂O to produce a syngasstream that is depleted in the soot.
 2. The process of claim 1 whichfurther comprises: (iii) recovering a portion of the heat from the sootdepleted syngas stream and using at least a portion of the recoveredheat to facilitate the additional production of syngas via the(endothermic) catalytic reforming of natural gas and steam.
 3. Theprocess of claim 1 wherein substantially all of the byproduct soot isgasified in step (ii).
 4. The process of claim 1 wherein thenon-carbonaceous material comprises alumina.
 5. The process of claim 1wherein the non-carbonaceous material contained in the second reactor isin the form of spherical particles.
 6. The process of claim 1 whereinthe non-carbonaceous material contained in the second reactor is in theform of rings.
 7. The process of claim 1 wherein the non-carbonaceousmaterial contained in the second reactor has a catalytic functionalityto facilitate the gasification of the soot.
 8. The process of claim 1wherein first and second reactors are operated in a temperature rangefrom 2100 F to 2800 F.
 9. The process of claim 1 wherein a fluid isadded to the syngas and byproducts produced by the first reactor priorto introducing the syngas and byproducts into the second reactor.
 10. Inan apparatus for the exothermic generation of syngas by the partialoxidation of a hydrocarbon-containing fuel comprising: (i) a firstreactor for reacting the hydrocarbon-containing fuel with an oxygencontaining gas to produce the syngas and byproducts comprising CO₂, H₂Oand soot; and (ii) a second reactor for receiving the syngas andbyproducts containing a non-carbonaceous material that traps the sootfor a sufficient time such that the majority of the byproduct soot isgasified via reaction with the byproduct CO₂ and/or H₂O to produce asyngas stream that is depleted in the soot.
 11. The apparatus of claim10 which further comprises: (iii) a heat exchange reformer forrecovering a portion of the heat from the soot depleted syngas streamand using at least a portion of the recovered heat to facilitate theadditional production of syngas via the (endothermic) catalyticreforming of natural gas and steam.
 12. The apparatus of claim 10wherein substantially all of the byproduct soot is gasified in thesecond reactor.
 13. The apparatus of claim 10 wherein thenon-carbonaceous material comprises alumina.
 14. The apparatus of claim10 wherein the non-carbonaceous material contained in the second reactoris in the form of spherical particles.
 15. The apparatus of claim 10wherein the non-carbonaceous material contained in the second reactor isin the form of rings.
 16. The apparatus of claim 10 wherein thenon-carbonaceous material contained in the second reactor has acatalytic functionality to facilitate the gasification of the soot. 17.The apparatus of claim 10 wherein first and second reactors are operatedin a temperature range from 2100 F to 2800 F.
 18. The apparatus of claim10 further comprising a means to add a fluid to the syngas andbyproducts produced by the first reactor prior to the second reactorreceiving the syngas and byproducts.